2-4 weeks is a good quarantine period. It really depends on the source where you got the fish. If it was a big box store then 100% you should keep a 4 week quarantine. If it was a personal transaction and you trust the persons tank where you got the fish then you should be able to put them in almost immediately. Personally, if it came from a store it needs to be quarantined.
Have you ever seen a French Ninja? NO because they are sneaky.